The prefilter module can be used
for shaping the tone of the audio prior to distortion, as well as adding LFO
(low frequency oscillator) and envelope
controlled filter effects.
The prefilter module provides three bands or filters as indicated by the three dark circles on the spectrum. You can independently select and set each of these three filters, apply LFO or envelope effects, or change the type of each filter.
Selecting a Filter Type
To select a filter type, first select a filter (a dark circle). Your selection will be highlighted by a cross appearing through the circle. Once you have a filter selected, click on the button labeled "Select..." to change the type.
A number of highpass, midrange (bandpass or peaking filters) and lowpass filters are provided with Trash. Depending on the filter type selected, you can set gain, width (slope) and/or resonance.
The filter types are modeled after specific analog filters, and as a result the parameters and frequency range differs depending on the filter type selected. For example, some filters such as the TalkBox filters have limited bandwidth. In this case, a shaded region indicates that this filter does not have any effect in this upper frequency range. For other filters, some may support bandwidth or Q control, some may support gain, and some may support resonance.
Setting a Filter:
You can adjust a filter by clicking on the dark circle that represents its location and dragging the crosshairs to change the parameters of the filter. You can also use the arrow keys to adjust a selected band, or the Shift key in combination with the arrow keys to adjust in larger increments.
Q/Bandwidth
For some filter types, if you move the mouse over the "handles" on the side of the filter, you can adjust the Q or bandwidth by dragging with the mouse and widening the band.
You can also use Page Up and Page Down keys to change the width of the band, or if you have a wheel mouse, you can use the mouse wheel to widen a selected band.
Resonance
For some filter types, if you move the mouse over the "handles" on the top and bottom of the filter, you can adjust the resonance by dragging the handle with the mouse and widening the band.
Sweeping Filters
The Prefilter module can provide "sweeping" filter effects as well. The sweeps can be controlled by an LFO, or low frequency oscillator, so that the sweep is based on a timed period. They can also be controlled by the envelope or level of the incoming audio, so that the sweep is triggered by higher levels in the audio.
LFO Sweeps
To create a sweeping LFO filter, select a filter and click the LFO button. Additional LFO controls appear in the upper right corner as shown below:
You can set the period or speed of the sweep with the Period control. Smaller periods are faster sweeps, where the period is by default displayed in milliseconds. In addition to entering the speed directly, you can tap the "Tap Tempo" button to automatically set the speed to the rate that you've tapped the button.
The shape of the sweep can be set by clicking on the shape button -- toggling between various waveforms such as sine, square, and triangle to set the shape of the controlling sweep.
The Options screen allows you to view and set the rate of the LFO in tempo (beats per minute) as opposed to milliseconds. Click on the Options button and set the LFO to display tempo. You can also have the LFO slider snap to integers of the tempo, allowing you for example, to easily go from full measure to half measure sweeps.
Finally, you'll want to set the position of the sweeping filter -- the target destination for the sweep. A filter can sweep in frequency, gain, resonance -- any parameter that can be set on a filter can be used as a "target destination" for a sweep. For example, you might have a filter that sweeps up and down in frequency, or one that sweeps to become wider and then more narrow.
To set a target destination, note that when you selected a filter and set it to LFO, an additional white circle appeared on the spectrum. That is your target filter -- you can position that filter in any location with any resonance or bandwidth, and your filter will sweep to that point. A red line connects a node with its target node, and a red dot on that line shows the current position of the modulation during playback.
Envelope Sweeps
Instead of sweeping to a timed LFO, you can sweep filters based on the level of incoming audio. This can create, for example, triggered "auto wah" effects.
To setup an envelope sweep on a filter, select a filter and click the Envelope button. Additional Envelope controls appear in the upper right corner as shown below:
Threshold: Sets the level at which the sweep will be triggered. A lower threshold will result in the sweep being triggered more often, as the level of the incoming audio will cross the threshold more often. Note that the threshold slider serves a dual purpose as a meter and a control, allowing you to see the level of the incoming audio as you adjust the threshold point.
Attack and Release: The attack sets the time that it takes the filter to sweep to its destination after the threshold is exceeded, while the release sets the time it takes for the filter to return to its original position after the level drops back down below the threshold.
Note that the threshold level is based on an RMS or
averaging of the audio for a more natural and consistent effect. You can set the
averaging time in the Options screen by changing the Envelope RMS Time
option.
Visuals
As you adjust a band you will see two EQ curves. The bright dark grey curve is the composite of all EQ bands while the lighter white curve shows the effect of the selected band.
A spectrum by default is overlaid on the pre-filter module for visual feedback
of the mix. You can turn off the spectrum to conserve CPU or if you just
don't want to see it by using the Options screen. You can also set options such
as average or real time spectrum, show peak spectrum, etc. See the Spectrum Options
screen here...
Tips and
Tricks
1) If you hold down the Alt key and click on the spectrum, you have an audio magnifying glass that lets you hear only the frequencies that are under the mouse cursor, without affecting your actual EQ settings. This is useful for pinpointing the location of a frequency in the track without changing your actual EQ bands. Releasing the mouse button returns the sound to the actual EQ. You can set the default bandwidth of this filter in the Options screen under "Alt-Solo Filter Q".
2) If you hold down the Shift key and drag an EQ band, the EQ band will be "locked" in the direction that you're dragging. So if you just want to change the gain without affecting the frequency (or vice-versa) just hold down the Shift Key while you drag.
3) If you've chosen to display an averaging spectrum or a peak hold spectrum (using the Options screen) you can reset the peak hold or the averaging by clicking on the spectrum.
4) Right-click (under OS X you can also ctrl-click) on the spectrum and select "Spectrum Options" to bring up an option dialog that controls the spectrum display. Learn more about these options here...
Note: This help file is a quick reference for basic Trash functions and controls. We have separate "how to" guides that provide tips and techniques for getting the most out of Trash. You can download these guides from http://www.izotope.com/products/audio/trash/guides.html